1. Field of the Invention
The present invention relates to a surface fastener obtained by molding a flat substrate and a plurality of engaging elements integrally and continuously using thermoplastic resin, and a manufacturing method and a manufacturing apparatus therefore. More particularly, it relates to an integral molded surface fastener in which the engaging elements are not likely to fall down despite their minute dimensions and engage fine pile pieces such as unwoven fabric securely so as to ensure a necessary engaging force, separation force and a high engaging ratio. Further, this surface fastener being capable of bearing repeated engaging/disengaging operations several times and preferable for particularly, a paper diaper, medical simple clothes, napkins, various kinds of working simple clothes, underwear and the like, and a continuous manufacturing method and a continuous manufacturing apparatus for the surface fastener are related to.
2. Description of the Related Art
In recent years, the surface fastener having a plurality of the engaging elements of minute dimension integrally on a flat substrate obtained by injecting thermoplastic resin continuously has been used in various fields as a fastener of a disposable paper diaper, medical simple clothes, napkins, various kinds of working simple clothes, underwear and the like. Forms of this kind of the engaging element of an integral molded surface fastener are divided largely to hook type and mushroom type as well known in a related filed.
A typical hook type integral molded surface fastener has been disclosed in for example, U.S. Pat. Nos. 4,984,339 and 5,537,723. According to these molded surface fasteners, molten resin is supplied to the circumferential face of a cylindrical drum, in which a plurality of substantially J-shaped cavities while each cavity is curved from an inside of the drum and opened to the circumferential face are formed, so as to mold a thin plate-like substrate along the circumferential face. At the same time, the cavities are filled with part of the molten resin so as to mold an inverted J-shaped hook integrally with the rear face of the substrate. After cooling, the molded product is separated from the circumferential face of the drum.
Further, an integral molded surface fastener having modified configuration of the aforementioned hook-type engaging elements has been also disclosed in for example, Japanese Patent Application Laid-Open No. 2-5947 and Japanese Patent Application Laid-Open No. 6-133808. In manufacturing these molded surface fasteners, molten resin is extruded from an extruding die having an opening erected in a substantially two-leaves palm tree or T-shape on a narrow slit extended in the horizontal direction so as to mold a multiple rows of ribs each having a palm-tree or T-shaped section in the extruding direction on a thin plate-like substrate, thereby providing a primary molded product. Next, the rib of the primary molded product is cut in a predetermined thickness in the length direction successively and the palm tree shaped or T-shaped engaging elements are formed closely. Then, the substrate is expanded in the molding direction so as to separate respective engaging elements at a desired pitch, so that a molded surface fastener having a final configuration is produced.
Recently, a molded surface fastener having a hook type engaging element, whose shape is novel and never seen before and provided by changing a configuration of the conventional hook type engaging element largely, has been developed. Those molded surface fasteners have been disclosed in for example, Japanese Patent Application Laid-Open No. 9-322812 and Japanese Patent Application Laid-Open No. 11-56413. The engaging elements disclosed in these publications comprise an erected portion which is erected upward from the surface of the substrate, a neck portion which is separated in the molding direction with a V-shaped gap at a top end of the erected portion and an engaging head extended substantially horizontally back and forth in the molding direction from the neck portion. Further, a bottom face of the engaging head is inclined obliquely upward toward a front end thereof and a top face of the engaging head is flat. Additionally, a wing-like expanded portion having a thickness predetermined vertically is expanded each from the right and left side of the top face portion as viewed from the front in the molding direction.
As for the basic manufacturing method, primary molding technology using the aforementioned cylindrical drum is applied. However, the engaging element to be molded on the surface of the substrate at the time of molding is not molded in a J-shape from the beginning, but by molding a primary engaging element material having a substantially Y-shape having two V-shaped branch portions at a top end of the erected portion, as viewed from the side in the molding direction. Then, a preliminary molded product having a plurality of the primary engaging element materials on the substrate is produced. Consequently, the branched portion of said primary engaging element material of the primary molded product is heated with pressure so as to be deformed, so that the aforementioned engaging element having a peculiar configuration never seen before is molded.
On the other hand, the mushroom type molded surface fastener has been well known since before. According to, for example, U.S. Pat. No. 3,192,589, a primary molded product in which a plurality of column portions are erected on the surface of the substrate is molded. After that, a front end of the column portion of the molded product is soften by heating so as to mold a semi-spherical engaging head, thereby producing a molded surface fastener. Further, for example, Japanese Patent publication No. 8-508910 has disclosed an improved technology of the mushroom type molded surface fastener. In the molded surface fastener disclosed in this publication, a front end of the column portion of the primary molded product is softened by heating with pressure, so that a disc type engaging head is molded instead of the aforementioned semi-spherical engaging head.
Because the aforementioned mushroom type engaging element engages in all directions, it has been well known that it ensures a higher engaging strength and separation strength than the hook type engaging element whose engagement has a directivity. However, the mushroom type engaging element engages pile with its engaging head such that the pile winds around the neck portion of the engaging element, that is, the pile is hung from the neck portion. Therefore, there is a high possibility that the engaging element may be cut at the neck portion or the pile itself may be cut out when it is intended to release the pile from the engaging head. Thus, this type of engaging element often cannot bear repeated use and the engagement strength and separation strength are likely to be excessively increased.
The molded surface fastener disclosed in the aforementioned Japanese Patent publication No. 8-508910 is improved based on advantage and disadvantage of the mushroom type engaging element. The configuration of the engaging head is formed in a substantially disc-shape so as to intensify engagement ratio with minute pile and its separation strength is set appropriate. Consequently, this molded surface fastener can be applied as a fastener for the minute pile in various kinds of unwoven fabric, which is attached to the aforementioned disposable diaper and the like. As described above, application of such a fastener has been expanded rapidly and a further improvement has been proposed in for example, International Publication WO98/57565. In the improvement, it is intended to increase plasticity of the engaging head by forming a plurality of minute unevennesses on the top face of the disc-shaped engaging head.
On the other hand, the hook type engaging element is more likely to engage the pile as compared to the mushroom type engaging element and capable of securing appropriate engagement strength and separation strength easily. Further, upon separation, the engaging element or the pile is never cut out and it can bear repeated use. To use this kind of the engaging elements in the disposable diaper by employing such an advantage, for example, the aforementioned Japanese Patent Application Laid-Open No. 6-133808 has proposed a flat rectangular sheet-like piece of the engaging head. According to the Japanese Patent Application Laid-Open No. 9-322812, the engaging head is extended in two directions, back and forth in the molding direction so as to raise the engagement ratio. Further, the top face of the engaging head is formed substantially horizontal while a bottom face thereof is formed such that the vertical thickness is gradually decreased as it goes to the front end. Furthermore, the configuration of the engaging head is devised so that an expanded portion having a necessary thickness is expanded from a top face portion of the engaging head to a direction perpendicular to the molding direction.
However only if the dimension of the engaging element is reduced to increase the density or the configuration of the engaging element is changed to a simple one like the molded surface fastener disclosed in the Japanese Patent Application Laid-Open No. 6-133808, there is no warranty that the shearing strength and separation strength upon joining mating unwoven fabric are increased even when the engagement ratio with the minute pile such as the mating unwoven fabric, knitted fabric or the like is increased. Further, when the density of the engaging elements is increased extremely, when it is intended to make the hook-like engaging head invade into extremely flexible fiber pile wooded thickly on a mating unwoven fabric, the fiber pile disposed at random falls down by the engaging heads or the engaging heads themselves fall down, so that invasion of the engaging head into the fiber pile is disabled. Therefore, the engagement ratio drops as compared to the engagement ratio in an ordinary surface fastener. Thus, in the molded surface fastener having the minute engaging elements, there are limits in miniaturization of the configuration of the engaging element and the density thereof.
According to the manufacturing technology of the engaging element disclosed in the same publication, a multiplicity of ribs erected on a substrate of a primary molded product formed primarily are cut out successively at a predetermined pitch in the longitudinal direction and then, the substrate is extended in the longitudinal direction (molding direction) so that individual engaging elements are spaced at a predetermined interval. Therefore, the thickness in the molding direction of the engaging element is determined by the pitch of the cutting out and its stiffness is determined depending on material of used resin and cutting thickness. Therefore, when it is intended to obtain an engaging element which engages and disengages the minute pile such as a surface of unwoven fabric according to such manufacturing method for example, the thickness of the engaging element in the molding direction needs to be decreased, so that it is likely to be distorted in the molding direction. Thus, its stiffness cannot be improved unless the thickness is increased.
Additionally, in the molded surface fastener having the hook type engaging elements disclosed in the Japanese Patent Application Laid-Open No. 9-322812 or Japanese Patent Application Laid-Open No. 11-56413, although the aforementioned falling down of the erected portion is decreased due to the peculiar configuration of the engaging element and the engagement ratio is secured, a necessary separation strength is more difficult to obtain as the miniaturization is intensified. Thus, in particular, increase of the separation strength to the aforementioned disposable diaper and the like has been strongly demanded.
On the other hand, in the molded surface fastener having the mushroom type engaging elements disclosed in the Japanese Patent publication No. 8-508910 or the International Publication WO98/57565, a stem portion having an arbitrary diameter can be molded in order to prevent its bending and apply a required stiffness, although it is minute. However, when it is intended to provide the stem portion with a required stiffness, the diameter of the stem portion necessarily must be increased. When the diameter of the stem portion is increased, even if the extending length of the engaging head extended in all directions from the stem portion is set minute, the diameter of the engaging head is necessarily increased by such an increased amount of the stem portion. As a result, the engaging head cannot engage such minute loops easily.
In any one of the engaging elements disclosed in the above-described publications, it is impossible to exclude a configuration and function peculiar to the mushroom type engaging element. That is, in any engaging element, the engaging head is extended in all directions around the stem portion, so that the pile is always wound around the neck portion upon the engagement or the neck portion is always hung by the pile. The separation strength by the engaging element itself is too high even if any improvement is made, so that the separation strength cannot be reduced to strength appropriate for a fastener of, for example, the disposable diaper. Further, it is difficult to avoid cutting of the pile.
As for a problem of this kind of the conventional integral molded surface fastener, when it is intended to use the fastener as a fastener in a disposable diaper, medical simple clothes, napkins, various kinds of working simple clothes, underwear and the like, it must cope with extremely minute pile exposed on the surface of, for example, ordinary unwoven fabric or knitted fabric as a counterpart for the engagement. Thus, each engaging element of the integral molded surface fastener must be formed in minute dimension and particularly, because the engaging elements are likely to come into contact with the mild skin of baby, they need to be plastic enough and mild in its texture to the skin. Further, this kind of fastener needs to bear repeated use of at least two or three times sufficiently even if it is disposable and at the same time, an appropriate separation strength not allowing the diaper to slip out easily is demanded.
However, although its engaging elements can be miniaturized in the conventional integral molded surface fastener, the engaging element such as the mushroom type engaging element still ensures a too strong separation strength, so that the minute pile and the engaging element itself are likely to be damaged upon separation. As for the hook type engaging element, although the minute pile and the engaging element itself are never damaged, currently, a required separation strength has not been secured.
The present invention has been achieved to solve those various problems and therefore, an object of the invention is to provide an integral molded surface fastener having minute and peculiar engaging elements, which engage fine and thickly wooded fiber pile securely while each engaging element secures an appropriate engaging strength, shearing strength and separation strength, wherein texture of a surface of the surface fastener is improved and the height of the engaging elements protruded from a surface of the substrate may be set lower than a conventional one, thereby preventing the engaging elements from falling down by a pressing force. At the same time, the engaging element of the invention secures a high engaging ratio with a mating pile piece and satisfies a durability required for this kind of fastener, and preferably, secures a desired plasticity and tearing strength of a flat substrate.
To achieve the above object, there is provided an integral molded surface fastener of synthetic resin having a plurality of fine engaging elements molded integrally on the surface of the flat substrate for engaging/disengaging mating pile pieces, wherein each of the engaging elements comprises a single column portion having a substantially cross-shaped section constituted of a first column portion and a second column portion each having a necessary height and a necessary width in an intersecting direction parallel to the surface of the substrate and substantially rectangular thin plate-like engaging heads formed in a top end portion of the column portion, having substantially the same width as the width of the top end of the second column portion, and being parallel to the surface of the flat substrate and extended in opposite directions along the width direction of the first column portion.
The substantially rectangular thin plate-like configuration mentioned in this specification includes not only complete rectangles but also configurations whose ends in a long side direction are extended outwardly and in which width of the long side is slightly changed.
Because according to the invention, the section of the column portion of the engaging element forms a substantially cross shape, stiffness in the width directions extending with cross-shape of the first and second column portions intersecting each other, that is, stiffness in four directions, is increased. Thus, difficulty of being bent of the column portion of the invention is not inferior to those of the column portions having a section of a square whose side has the same dimension as the width of the first or second column portion, or a section of a circle whose diameter has the same dimension as the width. That is, it means that the invention can secure a required stiffness more easily although the amount of material used is smaller if the same material is employed.
However, when the column portion is composed of a mere rectangular column portion, when it is pressed from above in order to engage it with a mating pile or it is intended to remove the engaged pile, the column portion is likely to fall down at its root. Thus, preferably, the width of at least any one of the first and second column portions is decreased gradually toward the engaging head, that is, the width dimension of the column portion near a proximal end thereof is increased so as to increase stiffness of that portion, thereby making it difficult for the column to fall down.
On the other hand, according to the invention, the engaging heads formed at the top end of the column portion, that is, the rectangular thin plate-like engaging heads each having the same width dimension as the width dimension of the top end of the second column portion is extended from the column portion as a center portion in the form of wing in the width direction of the plate of the first column portion, each engaging head having substantially the same dimension. In other words, in the engaging element of the invention, the center portion of a mule-like thin plate portion having the same width as the top end of the second column portion is supported by the top end of the column portion erected such that the first and second column portions intersects each other in the shape of a cross. The engaging element has a pair of the engaging heads extended in opposite directions from the top end of the first column portion substantially horizontally. This engaging element belongs to a modified type of the above-described hook type engaging element.
The vertical thickness of the engaging head may be determined arbitrarily according to the latter mentioned manufacturing method of the invention. However, it may be changed by the width dimension of the head, that is, the width dimension of the top end of the second column portion, or the size or configuration of the pile on the surface of the unwoven fabric, which is an engagement mate. Meanwhile, the height of the pile protruded from the surface of unwoven fabric or knitted fabric for use in a pile engaging portion of the disposable paper diaper and the like is as fine as about 0.35 to 1.1 mm.
Therefore, when the engaging head is formed with a small width dimension while the thickness thereof is as small as possible, the engaging head is allowed to invade into the above-described minute pile. However, when the thickness of the engaging head is too small while the width dimension thereof is also too small, a required engaging strength or separation strength cannot be secured. For the reason, it is very important that the thickness and the width dimension can be controlled arbitrarily.
However, in some case, no sufficient effect can be obtained only if the thickness or the width dimension is changed. Thus preferably, a bottom face of the engaging head is composed of a tapered face whose thickness is decreased gradually from the first column portion toward a front end of the engaging head. By applying such a structure, the vertical thickness of the front end of the engaging head is set smaller than that of the proximal end portion thereof. Thus, not only the engaging head can invade into the mating pile more easily but also if the pile engages, the engaging strength and separation strength are increased because the thickness near the proximal end portion is large. Meanwhile, as for the engagement aspect between the engaging head and the pile of the invention, the pile is entangled with a pair of the engaging heads at the same time so that it is hooked on the column portion of the engaging head.
Preferably, a top face of the engaging head is substantially flat. Because the top face of the engaging head is formed substantially flat, there is no prickly feeling peculiar to an engagement face of the molded surface fastener, so that an extremely smooth surface can be obtained thereby eliminating a danger of damaging the user""s skin.
Further preferably, the center portion of the top face of the engaging head in the longitudinal direction is formed such that it is slightly recessed with respect to the other top face portion. This recess makes it easy for the engaging head to be bent on the border between the recess and the engaging head extended from the first column portion, when it is intended to release the engaged pile from the engaging head. As a result, even if the thickness of the proximal end portion of the engaging head is large, the pile can be released from the engaging head easily. Consequently, necessary separation strength can be obtained.
Preferably, a further aspect of the configuration of the engaging head is specified and that is, each front end of the engaging head is curved downward. Although the basic configuration of the engaging head is of thin plate, the front end of the engaging head is curved downward according to this aspect. This curved portion allows the pile once engaged to be hooked on that curved portion, thereby increasing the engagement strength and separation strength.
Further preferably, the substrate is not composed of a mere flat plate, but a concave portion is further provided between adjacent column portions in a molding direction of the substrate.
Thus, when the engaging element is raised upward from the bottom face of the concave portion, even if a distance between a rear face of the front end of the engaging head and a starting end of the column portion (bottom face of the concave portion) is set as usual, the distance between the bottom end of the front end of the engaging head and the surface of the substrate other than the concave portion becomes equal to a difference between an actual height of the column portion from the proximal end thereof and the depth of the concave portion. Thus, although the actual height of the engaging element erected from the substrate is of the same dimension as conventionally, an apparent height protruded from the surface of the substrate is of the dimension that the actual height of the engaging element minus the depth of the bottom face of the concave portion.
If the concave portion is formed in the surface of the substrate, plasticity of the substrate is improved remarkably even if the apparent thickness is the same as conventionally. Further, regarding the molding thereof, when the surface fastener is peeled off from the molding die after the surface fastener is molded, it can be separated stably such that the substrate is not stretched unreasonably or torn out.
As a result, there is no waving in the substrate of a molded product, so that a high quality product capable of bearing actual use sufficiently can be obtained. If the height of the column portion from the bottom face of the concave portion is set substantially ⅕ to ⅘ of the height from the bottom face to the top of the front end of the engaging head, a portion of the column portion protruded from the surface other than the concave portion of the substrate is relatively lower. Thus, the column portion is more unlikely to fall down, thereby stabilizing the configuration upon engagement. Further, when the concave portion has such a width allowing a mating pile to be introduced therein, engagement ratio with the pile is increased.
As for a preferred dimension of the engaging element of the invention, particularly, a distance between the top of the front end of the engaging head and the surface of the substrate is 0.1 to 1.2 mm, the extending length of the engaging head from the column portion is 0.2 to 0.5 mm and the height of the column portion from the surface of the substrate is 0.005 to 1.0 mm. These numeric ranges are basic numeric ranges sufficient for securing the engagement with the pile piece (pile) having a minute configuration, which is an engagement object of the invention and further, the ranges produce no strict feeling upon engagement or disengagement. Particularly, their minimum values allow secure engagement with a fiber pile having the finest configuration in ordinary unwoven fabric.
Preferably, each dimension and density of the engaging element are specified. The maximum thickness in the vertical direction of the engaging head requires not so high stiffness if considering engagement strength or separation strength in case where the fastener is employed for the disposable diaper or the like, but the thickness of 0.2 to 1.1 mm is sufficient. More preferably, the front end of the engaging head is narrowed gradually as viewed from above, so that it becomes more likely to invade into the mating pile.
Further preferably, the dimension between ends in the extending direction of the engaging head is 0.4 to 1.2 mm while the maximum width thereof in a direction perpendicular to the extending direction from the first column portion is 0.2 to 1.2 mm. Alternately, the extending length of the engaging head from the first column portion is 0.08 to 0.5 mm. Further alternately, the height from the surface of the substrate to a top face of the engaging head of the engaging element is 0.1 to 1.2 mm.
If the total area of the top face of the engaging element is set to 20 to 50% of the surface area of the substrate, preferably, to 25 to 40%, not only the desired engagement ratio with the mating pile is secured, but also a prickly feeling, which may be generated when the engaging head of the surface fastener is touched, is eliminated. When a continuous molded surface fastener having the above described configuration is mounted on the paper diaper or the like through continuous process, the long molded surface fastener transferred continuously is cut out to a desired length in succession. This cut piece is rotated and moved by a suction roll having a fixed sucking portion provided on part of an inner wall face of its peripheral face with a rotation of the roll, such that the erected face of the engaging element is sucked. Then, the cut piece is carried to a predetermined position of the paper diaper carried through a transportation path disposed perpendicular to the rotation direction of the cut piece and mounted to the paper diaper successively. Therefore, the cut pieces need to be sucked and carried effectively and securely on the peripheral face of the suction roll. When the total area of a flat surface with respect to the surface area of the substrate is set up as described above, the suction to the suction roll is achieved securely.
Preferably, the arrangement of the engaging elements having such structure on the substrate is specified.
The first column portion is disposed perpendicular to the molding direction of the substrate while the second column portion is disposed parallel to the molding direction of the substrate. Alternately, the first column portion may be disposed parallel to the molding direction of the substrate while the second column portion may be disposed perpendicular to the molding direction of the substrate. To direct the engaging heads in two different directions, that is, the molding direction and a direction perpendicular thereto, it is preferable to turn the cavity portion composed of the long hole portion by 90xc2x0.
As a result, a case where engaging elements whose first and second column portions are formed in the both directions proposed above are mixed is specified. That is, engaging elements whose engaging heads are extended in the molding direction of the substrate and engaging elements whose engaging heads are extended in a direction perpendicular to the molding direction of the substrate exist mixedly. Because the engaging elements directed to the two directions, that is, the molding direction and the direction perpendicular thereto, exist mixedly, the engagement ratio with the mating piles is improved. The way of the arrangement may be determined arbitrarily, so those engaging elements may be disposed on the surface alternately in the form of matrix of the substrate or in a staggered way.
According to the invention, there is provided a manufacturing method for the aforementioned integral molded surface fastener having hook type engaging elements, comprising the steps of rotating in a single direction a cylindrical drum having a plurality of cavities for molding preliminary engaging elements each comprised of a cross-shaped section hole portion which is open in the shape of a cross on its peripheral face and extended up to a predetermined depth and a long hole portion extended in the molding direction or in a direction perpendicular to the molding direction, which is formed subsequently to the cross-shaped section hole portion and has a deep portion branched to two sections, molding preliminarily-molded elements each which is erected integrally with the rear face of the substrate and comprised of a preliminarily-molded column portion extended from a proximal end portion to an intermediate portion and having a cross-shaped section and a preliminarily-molded head extended from the preliminarily-molded column portion to a top end and having an elongated section with the top end portion branched to two sections by filling part of molten resin into the cavities at the same time of injecting of the molten resin toward the peripheral face of the cylindrical drum continuously and molding the substrate along its peripheral face, separating continuously a belt-like preliminarily-molded product having the preliminarily-molded element on the substrate transferred by the peripheral face of the rotating cylindrical drum from the peripheral face of the cylindrical drum, transferring the separated preliminarily-molded product continuously to a heating pressure portion, and deforming the preliminarily-molded head of the preliminarily-molded element erected integrally from the surface of the substrate of the transferred preliminarily-molded product to a flat rectangular thin plate by heating with pressure and melting by means of the heating pressure portion so as to mold the engaging heads at the top end of the column portion continuously.
The most characteristic structure proposed in the method of invention is the configuration of the cavity formed in the peripheral face of the cylindrical drum and the configuration of the preliminarily-molded element for the engaging element formed by the cavity. According to the configuration of this preliminarily-molded element, the preliminarily-molded material erected with a mere equal section from the rear face of the substrate is not molded unlike the conventional mushroom type, but this preliminarily-molded element is comprised of a preliminarily-molded column portion having a cross-shaped section at a substantially half portion on the side of a proximal end of the preliminarily-molded element and a preliminarily-molded head, in which a half portion on the side of the top end portion continuous to this preliminarily-molded column portion has a substantially uniform and elongated section while the top end portion is branched to two sections in the form of a substantially U.
This preliminarily-molded element is deformed by heating the top end thereof with a pressure, so that the engaging element having the aforementioned peculiar shape of the invention is molded. The preliminarily-molded column portion turns to the first and second column portions of the engaging element and the preliminarily-molded head of the top half portion is deformed with melting to a substantially rectangular thin plate extended in the width direction so as to mold the engaging head. The extending amount and thickness of this engaging head are determined depending on the amount of resin used for the preliminarily-molded head and the amount of deformation with melting by pressure upon heating with pressure. Therefore, by controlling the amount of resin of that deformed portion and the amount of the deformation by heating with pressure, the thickness and extending length of the engaging head can be controlled. Further, by selecting the width direction of the first column portion to be the molding direction and/or a direction perpendicular thereto, the direction of the engaging head can be changed arbitrarily as proposed above.
When the top end portion of the preliminarily-molded head is molded in the form of a substantially U, in case that a column portion has such a mere elongated section, the dimension of the center portion of the engaging head intersecting the width direction of the column portion is enlarged upon deforming the engaging head by heating with pressure subsequently, so that it approaches the shape of the mushroom type engaging element which is entirely elliptic and extended in all directions from the column portion. As a result, engagement with the pile has directivity in all directions thereby making it difficult to control the engagement strength and separation strength. Consequently, as disclosed in the above-described Japanese Patent publication No. 8-508910, the fine piles and engaging elements are likely to be damaged and the separation strength is likely to be increased, so that such a shape of the mushroom type engaging element is not preferable. Therefore, molding the top end portion of the preliminarily-molded head in the form of a substantially U is very important for forming the hook type engaging head in order to avoid the above problems.
According to the invention, there is provided a continuous manufacturing apparatus for the integral molded surface fastener comprising a cylindrical drum rotating in a single direction and having a plurality of cavities for molding the preliminary-molded engaging elements each comprised of a cross-shaped section hole portion which is open in the shape of a cross on a peripheral face and extended up to a predetermined depth and a long hole portion elongated in the molding direction or in a perpendicular direction of the molding direction, which is formed subsequent to the cross-shaped section hole portion and has a deep portion thereof being branched to two sections, a continuous injecting device for molding the substrate along the peripheral face of the cylindrical drum by injecting molten resin toward the peripheral face continuously and filling the cavity with part of the molten resin so as to mold preliminarily-molded elements each which is erected integrally from the rear face of the substrate and comprised of a preliminarily-molded column portion extended from a proximal end portion to an intermediate portion and having a cross-shaped section and a preliminarily-molded head extended from the cross-shaped section portion to a top end and having an elongated section with the top end portion branched to two sections, take-up means for continuously separating a belt-like preliminarily-molded product having the preliminarily-molded element on the substrate transferred by the peripheral face of the rotating cylindrical drum from the peripheral face of the cylindrical drum and a heating pressure portion for deforming with melting the preliminarily-molded head of the preliminarily-molded element erected integrally from the substrate surface of the separated preliminarily-molded product to a flat rectangular thin plate by heating with pressure so as to mold the engaging heads continuously.
By disposing the continuous injection device, the cylindrical drum, the take-up means and the heating pressure portion described above, continuously, the molded surface fastener of the invention, in which a plurality of the engaging elements each having the above-described configuration are formed integrally on a continuous substrate can be manufactured effectively and continuously.
Preferably, the heating pressure portion comprises a mounting/transferring face for the preliminarily-molded product and a heating pressure roll having a shaft included in an upper plane parallel to and above the mounting/transferring face and extended in a direction perpendicular to the transferring direction of the preliminarily-molded product, a gap between a lower end position of the heating pressure roll and the mounting/transferring face being smaller than a sum of total dimension in the vertical direction of the substrate and the column portion and a dimension in the vertical direction of the engaging head. Alternately, the heating pressure portion comprises the a heating member, which is disposed above the mounting/transferring face and has an inclined face in which a gap between its lower face and the mounting/transferring face is decreased gradually instead of the heating pressure roll, and the minimum gap between the mounting/transferring face and the inclined face is smaller than a sum of the dimensions in the vertical direction of the substrate and column portion of the primary molded member and the dimension in the vertical direction of the engaging head.
**When the minimum gap between the pressing face of the heating pressure portion and the surface of the substrate is set up as described above, the engaging head having the aforementioned configuration can is formed only by introducing the preliminarily-molded product formed on the rotating drum into the heating pressure portion and passing by. Here, the minimum gap between the pressing face of the heating pressure portion and the surface of the substrate is set up to be the thickness of the engaging head, which has been preliminarily set up, when the preliminarily-molded head is deformed under a pressure. When the gap is slightly large, the portion corresponding to the elongated portion on the border region between the preliminarily-molded head and the preliminarily-molded column portion is not deformed so that it is left as a neck portion having the elongated section parallel to the width direction of the first column portion.
It is needless to say that a case where such a neck portion is formed is included in the technical scope of the present invention. When the mating pile engages the engaging head such that it winds around its neck portion if a neck portion having the elongated section in the extending direction of the engaging head is formed, when it is intended to remove that pile, the neck portion swings so as to incline the pile in the separation direction, thereby facilitating removal of the pile as compared to the case of non-existence of the neck portion and preventing the pile from being cut out unreasonably.
When the heating temperature of the heating pressure portion is adjusted near a melting point of material resin or the heating time with pressure of the preliminarily-molded product is prolonged, softening of the extending end of the engaging head is accelerated, so that it is curved downward and drooped due to its own weight and engagement force with the mating one is increased.
Upon molding the preliminarily-molded product according to the manufacturing method of the molded surface fastener of the present invention, cooling means is incorporated in, for example, a cylindrical drum and the preliminarily-molded product accompanying region of the cylindrical drum is dipped into the cooling bath and cooled positively. Preferably, the molded surface fastener passing the heating pressure means is not cooled positively by any special cooling means but cooled gradually in the ambient temperature and wound up as a final product. By cooling the engaging head deformed by heat gradually so that it hardens, crystallization of the same heated portion is accelerated so that stiffness of the engaging head is increased as compared to the column portion. At this time, a heating region, heating time and heating temperature can be controlled appropriately depending on the dimension and modification of the engaging element.
In the integral molded surface fastener in which the substrate and the preliminarily-molded elements are cooled and hardened rapidly without acceleration of crystallization, the substrate and column portion hold plasticity and the stiffness of the engaging head is increased. Thus, even in case of the molded surface fastener composed of minute engaging elements and having a high plasticity, the stiffness of the engaging head is secured so as to improve bending strength. Consequently, a molded surface fastener of the present invention, which has a predetermined engagement strength and separation strength as well as a resistance in the shearing direction, is obtained.